How to override private var in superclass - swift

Question

So I have the following superclass:
class Vehicle {
private var _maxSpeed: Int = 100
var maxSpeed: Int {
get {
return _maxSpeed
}
var tooFast: Bool {
get {
if maxSpeed >= 140 {
return false
} else {
return true
}
}
}
}
Plus I have some subclasses in which I want to override maxSpeed... per example:
class SuperCar: Vehicle {
//override the maxspeed...
}
But how should I approach this? Or is this only possible if we don't make it private? I tried to throw the private part out of the window but that won't work as well...
class Vehicle {
var maxSpeed: Int = 100
var tooFast: Bool {
get {
if maxSpeed >= 140 {
return false
} else {
return true
}
}
}
}
class SuperCar: Vehicle {
// override the maxSpeed...
override var maxSpeed: Int = 200
// Will not work...
}

Answer 1

Just put the class and subclass in the same file. private has nothing to do with inheritance. It has to do with file scope. Anything in the same file has access to private members.
That said, you almost certainly shouldn't be using inheritance here. Vehicle should almost certainly be a protocol. Then you wouldn't have any of the headaches of inheritance or private.
protocol Vehicle {
var maxSpeed: Int {get}
}
extension Vehicle {
// Default implementation if none is given
var maxSpeed: Int { return 100 }
// Another method that applies to all Vehicles
var tooFast: Bool {
return maxSpeed < 140 // (feels like this should be >= 140, but matching your code)
}
}
struct SuperCar: Vehicle {
// override the default implementation for the protcocol
var maxSpeed = 200
}

Answer 2

Set your private member variables in the init method
class Vehicle{
private var maxSpeed: Int
init(maxSpeed: Int = 100){
self.maxSpeed = maxSpeed
}
}
class SuperCar: Vehicle {
override init(maxSpeed: Int = 200){
super.init(maxSpeed: maxSpeed)
}
}

Answer 3

For a Swift 3 version of Rob's answer, you can't override private, but interestingly you can with fileprivate computed properties. You have to put the class in the same file though.
I did this today:
protocol Renderer {
}
class BaseClass {
private let _renderer: Renderer = BaseClassRenderer()
fileprivate var renderer: Renderer {
return _renderer
}
}
class Subclass: BaseClass {
private let _renderer: Renderer = SubclassRenderer()
override fileprivate var renderer: Renderer {
return _renderer
}
}

Answer 4

you can override computed property
class C {
var a: Int { return 10 }
}
class D:C {
override var a: Int { return 100 }